When oils (e.g. cooking oil, frying oil, fat, shortening, etc.) are exposed to high temperatures, particularly in the presence of oxygen and/or water, oxidative reactions can take place that result in degradation of the oils. Thus, oil quality is often monitored in restaurant kitchens, so as to determine whether the oil is still suitable for use. Historically, several different parameters have been used to evaluate the oil quality.
One parameter often used to evaluate oil quality is the total polar compound content of the oil. Onwumere et al., for example, disclose in U.S. Pat. No. 7,132,079 a method for determining whether or not to discard a sample of oil based on the presence of polar compounds in the oil. Mittal et al., for example, disclose in U.S. Pat. No. 5,818,731 a method and apparatus for measuring quality of oil. The method includes in part the comparison of a measured capacitance to a reference capacitance and relates changes thereof to an increase in the amount of polar molecular constituents of the oil.
Another parameter often used to evaluate oil quality is the free fatty acid content of the oil. Mlinar and Neumayer, for example, disclose in U.S. Pat. No. 4,654,309 an article for testing liquid for free fatty acid content. Free fatty acids may themselves comprise a portion of the total polar compound content of an oil sample, or may be precursors to such compounds as may be measurable in a test of total polar compound content. Thus, free fatty acid tests and total polar compound tests may not be completely independent. However, both tests have found use in the art.